1. Field of the Invention
The present invention relates generally to a cooling structure of gas turbine combustor and more particularly to a cooling structure in which a high temperature portion to be cooled of gas turbine combustor, such as a wall portion and a pilot cone, is made in a double structure of an outer plate and an inner plate so that cooling medium, such as air or steam, flows therein with enhanced cooling efficiency.
2. Description of the Prior Art
FIG. 17 is a schematic cross sectional side view showing structure of a gas turbine combustor and a cooling system thereof in the prior art, wherein FIGS. 17(a) and 17(b) show examples of air cooled system and FIG. 17(c) shows an example of steam cooled system. If description thereon is outlined, in FIG. 17(a), numeral 100 designates a pilot nozzle, which injects pilot fuel for combustion thereof, numeral 101 designates a main nozzle, which, being called an annular nozzle type, is arranged in plural pieces around a pilot inner tube 102 and injects main fuel to be ignited by combustion of the pilot fuel in the pilot inner tube 102. Numeral 103 designates a main inner tube, numeral 104 designates a connecting tube and numeral 105 designates a tail tube, and combustion gas of high temperature produced by combustion of the main fuel flows through these portions to be led into a combustion gas path of gas turbine. Numeral 106 designates an air by-pass valve, which causes surplus air coming from a compressor at a low load time to enter the tail tube 105 via a by-pass duct and to escape into the combustion gas path. In said type of combustor, there is employed a cooling structure using air in a wall of the tail tube 105, as described later with reference to FIG. 18.
In a combustor of FIG. 17(b), which is called a multiple nozzle type, numeral 107 designates a pilot nozzle, and a main nozzle 108 is arranged in plural pieces therearound. Main fuel is injected from the main nozzle 108 into an inner tube 109 to be ignited by combustion of pilot fuel injected from the pilot nozzle 107. Numeral 110 designates a tail tube and numeral 106 designates an air by-pass valve. In this type of combustor also, wall interior of the tail tube 110 is cooled by air, as described later with reference to FIG. 18.
Combustor of FIG. 17(c) is an example where a steam cooled system is employed in the multiple nozzle type combustor.
In FIG. 17(c), numeral 111 designates a pilot nozzle, numeral 112 designates a main nozzle, which is arranged in plural pieces around the pilot nozzle 111, and numeral 113 designates a swirler holder. Numeral 114 designates a tail tube, which is made integrally with an inner tube and is connected to the swirler holder 113 so that combustion gas of high temperature is led therethrough into the combustion gas path of gas turbine. In a wall of the tail tube 114, there are provided a multiplicity of steam passages for cooling therearound. Numeral 115 designates a steam supply passage and numerals 116, 117 designate steam recovery passages, respectively. Steam 200 for cooling flows through the steam supply passage 115 to be supplied into the steam passages in the wall of the tail tube 114 for cooling of wall interior thereof and is then recovered into the steam recovery passages 116, 117 provided at respective end portions of the tail tube 114 as steam 201, 202 to be returned to a steam producing source for an effective use thereof.
FIG. 18 is a partially cut away perspective view of the wall of the combustor tail tubes 105, 110 shown in FIGS. 17(a) and 17(b). In FIG. 18, the wall is made in a double structure in which an outer plate 120 and an inner plate 123 are jointed together being lapped one on another. The outer plate 120 constitutes an outer surface of the tail tube and has a multiplicity of grooves 121, each having a common cross sectional shape, provided therein substantially along a flow direction of the combustion gas. The outer plate 120 is jointed together with the inner plate 123 so that opening faces of the grooves 121 of the outer plate 120 are closed in the jointed plane. Also, in the outer plate 120, there are bored a multiplicity of air inlet holes 122, each communicating with the grooves 121 and being arranged with a predetermined interval between the air inlet holes 122 along each of the grooves (2).
The inner plate 123 has a multiplicity of air outlet holes 124 bored therein so as to communicate with the grooves 121 of the outer plate 120, when the outer plate 120 and the inner plate 123 are so jointed together. Each of the air outlet holes 124 is provided so as to be arranged in a mid position of two mutually adjacent air inlet holes 122 along each of the grooves 121. The outer plate 120 and the inner plate 123 are made of a heat resistant material, such as Hastelloy X, Tomilloy and SUS material, and the jointing thereof is done by diffusion welding in which a hot pressure welding is done under heat and pressure.
In the mentioned wall structure, air 300 for cooling entering the air inlet holes 122 from around the tail tube flows into the respective grooves 121 for cooling of the wall interior and flows out of the air outlet holes 124 of the respective grooves 121 to enter the tail tube as air 301. Such grooves 121, and air inlet holes 122 and air outlet holes 124 both communicating with the grooves 121, are provided in plural pieces in the entire circumferential wall of the tail tube and the air outside of the tail tube is supplied thereinto to flow in the wall interior for cooling of the entire portion of the tail tube wall and flows out of the respective air outlet holes 124 to be mixed into the combustion gas in the tail tube.
FIG. 19 is an enlarged cross sectional side view of the steam cooled type combustor shown in FIG. 17(c). As shown there, the swirler holder 113 of combustor, which is fitted to a turbine cylinder 130, is coupled with the tail tube 114 which is made integrally with the inner tube. In an entire circumferential wall of the tail tube 114, there are provided a multiplicity of steam passages 118, 119 substantially along a flow direction of the combustion gas. Each of the steam passages 118, 119 has a common cross sectional shape and communicates with the steam supply passage 115. A portion of the steam 200 in the steam supply passage 115 is supplied toward the nozzle side through the steam passages 118 for cooling of the wall to be recovered into the steam recovery passage 116 as the steam 201. Remainder of the steam 200 is supplied toward the downstream side through the steam passages 119 for cooling of the wall to be recovered into the steam recovery passage 117 as the steam 202.
FIG. 20 is a cross sectional side view of an upper half portion of a pilot cone fitted to an end each of the pilot nozzles of the combustors shown in FIGS. 17(b) and 17(c). In FIG. 20, the pilot nozzle is provided in the central portion of the combustor inner tube and a pilot cone 130 is fitted to an end of the pilot nozzle. The pilot cone 130 opens in a funnel-like shape, as shown there, and a guide ring 131 is provided around the pilot cone 130 for support thereof. For supporting the pilot cone 130 fixedly, welding is applied to around a connecting portion 132 between the pilot cone 130 and the guide ring 131 with a predetermined interval between the welded places.
In the central portion of the pilot cone 131, pilot fuel injected from the pilot nozzle burns and combustion gas 140 of high temperature flows there. A portion of the combustion gas 140 flows along a tapered wall inner surface of the pilot cone 130 and this wall inner surface is continuously exposed to the high temperature gas. Further, as mentioned above, the plural main nozzles are arranged around the pilot cone 130 and fuel injected therefrom is ignited for combustion by flame of the combustion gas 140 flowing out of the pilot cone 130, hence an outer surface of the pilot cone 130 and the guide ring 131 also are exposed to the high temperature.
Numeral 141 designates air, which flows out of a gap between the pilot cone 130 and the guide ring 131. While this air 141 flows out originally aiming at cutting off flame generated at an outlet end portion of the pilot cone 130 so that it may not continue, the air 141 carries out secondarily a convection cooling of the wall surface of the pilot cone 130 in the process of flowing through the gap between an outer wall surface of the pilot cone 130 and the guide ring 131 to thereby keep the pilot cone 130 cooled. Thus, in the prior art gas turbine combustor, while the tail tube is cooled by air or steam flowing in the grooves for cooling provided in the double structure of the tail tube wall, the pilot cone 130 is cooled by the air 141 flowing on the outer wall surface thereof.
In the mentioned prior art cooling structure of a high temperature portion to be cooled of gas turbine, such as a combustor tail tube, the grooves in the wall are provided having a common cross sectional shape each of the grooves and being arranged linearly in either of the air cooled system and the steam cooled system. For this reason, in order to satisfy a necessary cooling range at a portion where a uniform cooling is needed in the tail tube wall of a short section, a considerable number of linearly arranged cooling grooves are necessarily provided, and yet the cooling medium is discharged before it is fully used of its cooling ability because of the short cooling section, which results in the inevitable use of the cooling medium of more than needed. Also, because the cross sectional shape of the cooling groove is constant, flow velocity, pressure loss and heat transfer rate of the cooling medium are governed by the cross sectional shape, so that the cooling conditions of the cooling medium in the cooling passages from the inlet hole to the outlet hole thereof are decided monovalently by the cross sectional shape, thereby no adjustment thereof can be done, which makes optimized designing difficult.
Also, in the pilot cone which is likewise the high temperature portion to be cooled, while the cooling system thereof is such that the cooling is done by air flowing on the outer wall surface thereof, inlet gas temperature of a modern gas turbine becomes higher gradually, thereby environment of using the combustor is becoming severer year by year. Especially in the multiple pre-mixing type combustor, combustion vibration is becoming a problem. While it is confirmed effective to raise a ratio of pilot fuel as one of countermeasures to mitigate the combustion vibration, if the ratio of pilot fuel is so raised, it leads to an increase of thermal load in the pilot cone wall surface and to an insufficiency of the cooling ability unless the structure thereof is improved. Hence, measures to raise the cooling effect are desired.